Stock-Based Compensation - Stock Options (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term	10 years
Options granted (in shares)	0	0
Weighted average grant-date fair value of options granted (in dollars per share)		$ 1.44
Options exercised (in shares)	465,232	40,976	0
Total unrecognized compensation costs	$ 0
Liability awards	$ 1,300,000
Time Based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Options granted (in shares)	0
Options exercised (in shares)	338,133
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of option exercised (in shares)	$ 5,100,000	$ 200,000